1. Field of the Invention
The present invention is concerned with an arrangement for adjusting the diameter of a gas turbine stator.
2. Description of the Background
Today some gas turbines include adjusting devices to adjust the inside diameter of a stator in order to reduce the existing play between the stator and the mobile ends of rotor blades to the lowest possible value. A frequent device used to provide this diameter adjustment includes taking a portion of fresher gases originating in compressors, conveying the portion through the stator and blowing the portion onto stator driving rings extending in front of rotor blades. This makes it possible to carry out what is referred to as stator ventilation, the diameter of the stator being modified according to the temperature and flow of ventilation gases. Generally, the bleeding of gas is dual: one source known as a hot source with a fixed flow dilates the casing when necessary, while another source known as a cold source with a variable and controlled flow contracts the casing.
The path that the hot source ventilation gases use is a volume internal to the stator between the rings to be ventilated and the casing that surrounds them. Spacers linking the rings to the casing include transverse walls breaking the volume of the path into chambers, and through which it is necessary to create communication to make it possible for the ventilation gases to flow. Numerous examples of such communication means have been suggested in the prior art, but a good ventilation is not easy to ensure because it must be well distributed between successive rings and on the surface of each of these rings, otherwise the differences of ventilation intensity and of thermal dilation around the rings circumference will produce undulations of rings, and thus leave areas of gas escapes at the ends of the rotor blades. Moreover, openings arranged through the spacers weaken the rings, with dangerous consequences for portions of the machine subjected to strong mechanical stress, because stresses are concentrated around these openings.
The purpose of this invention is thus to suggest a gas turbine stator arrangement, the inside of which is compartmentalized, but provided with openings allowing ventilation gas to be blown onto the rings of the stator subjected to an adjustment. The openings are designed to produce a highly regular ventilation around the rings without exaggeratedly weakening structural elements through which they are drilled.
The present invention in its most general form relates to an arrangement for adjusting the diameter of a gas turbine stator. The stator includes a casing, rings bordering a vein of flowing gases and located in front of respective levels of mobile blades of a rotor, the rings being surrounded by the casing and fixed to the casing by circular spacers. Each ring includes a transversal wall extending from the casing to one of the rings and separating two chambers. The wall includes an outside edge curved into a spacer hook and engaged between a main portion of the casing and a respective appendage curved into a casing hook associated with the spacer hook. Communication paths of gas under pressure exist between chambers. At least one of the communication passages is carried out by cavities provided through a junction of hooks made up of one spacer hook and the casing hook with which it is associated.
Because spacer hooks and casing hooks are appendages or ends of these structures, they are subjected to moderate stress and the creation of openings through them produce acceptable levels of stress. Preferably, the communication means between chambers suggested herein include longitudinal notches cut through each spacer hook, a circular space located under the respective casing hook and outside the spacer hook, and radial notches made into the spacer hook between the longitudinal notches and the opening in the aforesaid chambers.
Two main designs of this arrangement are suggested: either radial notches are sufficiently deep to extend beyond the hook of the casing, or they include collecting portions followed by drillings; this last fitting lends itself readily to a calibration of the flow of ventilation (according to the intake section of the radial notches or drillings) and to the calming of gas in the chamber downstream from the flow (after passing through the tightened portion of drillings).